When there's no response you'll get a blank entry (may update this to display a * so it looks more like the command-line). The traceroutes are done with ICMP for now (eventually I'd like to implement it as a TCP port-80 traceroute but that's a lot harder to do on Windows than it should be).

My guess is that it is related to rewrite and the code isn't creating the non-rewrite version of the traceroute url correctly. If you navigate to /traceroute.php (I think that's it) you should see the UI.